1. Field of the Invention
The invention relates to a method for transmitting image bit stream and an image encoder and, more particularly, to a method for improving the transmission performance of image bit stream.
2. Description of the Prior Art
For image capturing products, such as digital cameras, mobile phones and so on, Joint Photographic Experts Group (JPEG) is one kind of image formats in common at present. With the promotion of image resolution and image quality, the size of JPEG bit stream is increased accordingly. Because the size increases, much time is required for transmitting the bit stream from memory to a storage device. For this reason, how to improve storing performance and transmitting rate of JPEG bit stream for users becomes a significant mission.
Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating an image capturing system 1 of the prior art. As shown in FIG. 1, the image capturing system 1 comprises a sensor 10, an image signal processor 11, a JPEG encoder 12, a bus 14, a memory 16 and a non-volatile storage 18. The sensor 10 is used for capturing an image. The image signal processor (ISP) 11 is used for processing the captured image and then transmitting the captured image to the JPEG encoder 12. Afterward, the JPEG encoder 12 compresses the captured image into image bit stream and then transmits the image bit stream to the memory 16 through the bus 14. The image bit stream stored in the memory 16 also can be written into the non-volatile storage 18 via the bus 14.
In the prior art, many methods can be adopted for improving the transmitting performance of the JPEG bit stream; one is to utilize a pipeline for compressing JPEG image into image bit stream and transmitting the image bit stream, to further increase the storing performance of the JPEG bit stream, as disclosed in U.S. Pat. No. 7,027,665. In this method, a controller of a storage device can store the bit stream while a JPEG codec compresses the image. The method utilizes the pipeline built between a codec and a storage device for reducing the required time of capturing image. By utilizing the pipeline, image procession and compression are unnecessary to be fully completed while a user is browsing an image. Besides, another method is to utilize a more effective bus and controller of a storage device for promoting the storing performance between memory and storage devices.
Furthermore, another method is disclosed in U.S. Pat. No. 6,167,153. In this method, although the method is used for increasing the JPEG compression rate, the real bottleneck is the transmitting performance of image bit stream between the memory and the storage device because of storing characteristic of memory. Some image device utilizes lots of memory buffer attached to the compressed image for promoting the storing performance, but the memory will be spent easily after capturing several frames. Accordingly, if the transmitting rate of the image data can be increased, the performance of the image capturing system can be promoted apparently.
Accordingly, the main scope of the invention is to provide a method for transmitting image bit stream and an image encoder to solve the aforesaid problems.